Abstract:
Microencapsulation of geraniol and wintergreen oil by the maize protein, zein, was investigated. The efficiency of encapsulation, the morphology of micro-particles and the controlled-release kinetics of the geraniol-zein system were studied.
The main findings were the following:
? Geraniol-to-zein mass ratios lower than unity showed very low particle yields. At ratios higher than unity an abrupt increase in particle yield was observed. It reached values as high as 85%. Concurrently high geraniol mass fractions up to 78% were realised. This unusual behaviour is proposed to be attributed either to the inversion of the zein globular structure driven by an increase in the hydrophobicity of the surrounding medium or to the increased phase separation kinetics of the geraniol.
? Insignificant particle yields for the wintergreen oil-zein system may be attributed to the high polarity of methyl salicylate.
? Geraniol and wintergreen oil-containing micro-particles had a spherical geometry prior to lyophilisation. Scanning electron and confocal microscopy revealed that the geraniol-zein micro-particles can be classified as reservoir systems. Release kinetics approaching zero-order release, consistent with a glassy reservoir system, were observed.
? Kinetic modelling predicts that 80% of encapsulated geraniol can be released over a period of 17 days at 20 ?C.
? The results mean that the geraniol-zein microcapsule system holds promise and that it should be possible to produce it for large-scale, sustainable agricultural use as an aphid repellent.
It is recommended that the release kinetics of the geraniol-zein system be studied in an aqueous environment and that other polar biopolymers be investigated.
